An example of vibration damping floor structure is shown in Japanese Patent Laid-open publication No. 10-317658. The vibration damping floor structure disclosed by this publication employs square cylindrical pipes or C-type steel frames having smaller cross sectional size and thickness than that of H-type steel frames. Ball bearings are installed in the square cylindrical pipes or C-type steel frames at predetermined locations. Thus, the example of this vibration damping floor structure achieves low cost, low floor height, low weight, and a short construction time.
In such a conventional vibration damping floor structure, a plurality of ball bearing supports are formed on the frame structure, and only one ball bearing is installed on each ball bearing support. Therefore, there is a problem in that a bearing force is insufficient for a large load. In the case where two or more ball bearings are installed on each ball bearing support, it is preferable that all of the ball bearings contact the surface of the concrete floor of the building. However, because there are inclinations or irregularities on the concrete floor surface, there is a problem that it is usually not possible for all of the ball bearings contact the floor surface.